"You are watching a star being born," says Kick-Ass director Matthew Vaughn about Chloe Moretz in the voiceover commentary to the DVD and Blu-ray release of the movie, which came out at the beginning of this month.

He's absolutely right. Once she appears on screen as Mindy, a/k/a Hit-Girl, the 11-year-old vigilante, even Nicolas Cage, who plays her father, can't keep up. Her first scene is one of cinema's great character debuts.

Not everyone is enthusiastic. Some complain that it's inappropriate for a child to disembowel enemies and utter four-letter words, even in a parody. They probably won't be mollified by Let Me In, Matt Reeves's remake of Swedish director Tomas Alfredson's Let the Right One In (2008), in which Moretz plays a 500-year-old vampire who is forever 13 years old. (It's set to open October 1.) Meanwhile, her career continues. I spoke to Moretz, who herself is now 13, on the phone while she was in London shooting The Invention of Hugo Cabret, Martin Scorsese's 3-D adaptation of Brian Selznick's bestselling children's book.

WhenKick-Ass first came out, some people were disturbed that an 11-year-old was killing people and using foul language.
Well, I mean, it's just a character. It was totally different from who Chloe is. And the film is rated R — it's not made for 11-year-olds. It's made for people of the age to be able to see the film.

I understand you were inspired to make it by Angelina Jolie inWanted.
Yeah! I'd always wanted to do a really fun action film with an Angelina Jolie–type character. And it was around when Wanted came out, and the billboards were everywhere, and everyone was talking about how amazing she is. So, basically, we got the script for Kick-Ass after I told my mom, "I really want that type character," and she was like, "It's exactly what you've been looking for." And I tried out for it, and Matthew thought I was the one, and we went for it.

The people who are upset by Hit-Girl probably won't be any happier with Abby, your character inLet Me In.
Hmm. It's just like Hit-Girl — it's a character, and it's far far far far far far away from who Chloe is, obviously. I'm not a vampire or an assassin or anything. I just say, put all the controversy aside and go see the film, and see if you like it. And I always say that after you see this film, you won't want to be a vampire. It's deeper, it's darker, and it's grittier than any other vampire film you've ever seen.

What do you think is the appeal of vampires?
Well, they're so special. They're these beautiful beings, and at the same time they have dark secrets. The way they live is so different from humans.

Speaking of beautiful beings — I read that Justin Bieber is your Twitter pal now.
Yeah, we tweet back and forth now and then. He's a cool guy.

You're working with another cool guy, Martin Scorsese. How is that going?
I'm actually in London right now, and it's going really well. Marty's such an amazing director, it's a privilege to be able to work with him.

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